Should measles vaccine be given at six months instead of nine for infants?

There is now an imminent threat of measles spreading in various regions globally, as COVID-19 led to a steady decline in vaccination coverage and weakened surveillance of the disease, the World Health Organisation (WHO) and the US Centers for Disease Control and Prevention(CDS) said last week.

Measles is a highly contagious and serious disease caused by a virus.

According to the WHO, before the introduction of measles vaccine in 1963 and widespread vaccination, major epidemics occurred approximately every 2–3 years and measles caused an estimated 2.6 million deaths each year

Measles is caused by a virus in the paramyxovirus family and it is normally passed through direct contact and through the air. The virus infects the respiratory tract, then spreads throughout the body.

While the vaccines against Covid were developed and needed to be given worldwide in an emergency, this had a negative fallout on the other immunisation programmes including measles. Experts have maintained that there is an urgent need to get the immunisation campaigns for other diseases back on track. There should be locally tailored methods by which the immunisation of measles gets a wider coverage.

The WHO and the CDS say measles immunisation has dropped significantly since the coronavirus pandemic began, resulting in a record high of nearly 40 million children missing a vaccine dose last year.

In a latest report, the UN health agency maintained that millions of children were now susceptible to measles, which is one among the world’s most contagious diseases.

In 2021, according to the WHO, there were an estimated 9 million cases and 1,28,000 deaths from measles alone globally.  A total of 22 countries experienced large and disruptive outbreaks.

“Decline in vaccine coverage, weakened measles surveillance, continued interruptions and delays in immunisation activities due to COVID-19, as well as persistent large outbreaks in 2022, certainly mean that measles is an imminent threat now at every region of the world,” the WHO noted.

The symptoms of measles start with high fever followed by runny nose, cough and then rashes. Unvaccinated young children are at highest risk of measles and its complications, including death.

The Way Forward

Experts have stressed on an urgent need to strengthen the surveillance systems, map the children who are not yet immunised and get them vaccinated at the earliest. Another important suggestion that has come forth was to give the vaccine at 6 months instead of the mandated 9 months.

The MMR (mumps, measles and rubella) vaccination, of which the measles vaccine is an important component, is given to children in two doses. The first at 9-12 months and the second around 3 years.

Amid the surge in measles in some states in India, the central government   has already recommended a shot of measles vaccine for children between 6 months and 5 years of age living in the affected areas.  The recent outbreak in many states only prompted the experts to recommend this “zero dose” for kids in the 6 month-to-9-month age bracket. According to reports, this will only be done in areas where kids in this age group make up for around 10 percent of total measles patients.

However, it is yet to be scientifically validated that giving a vaccine at 6 months can be really helpful or not. And, the real concern is whether it will have an adverse impact on the immune response to the later doses.

According to a study published in Lancet, vaccinating infants with a first dose of measles-containing vaccine (MCV1) before 9 months of age in high-risk settings has the potential to reduce measles-related morbidity and mortality. However, there is concern that early vaccination might blunt the immune response to subsequent measles vaccine doses.

The study, titled, Effect of measles vaccination in infants younger than 9 months on the immune response to subsequent measles vaccine doses, systematically reviewed the available evidence on the effect of MCV1 administration to infants younger than 9 months on their immune responses to subsequent MCV doses.

Vaccination with a MCV before 9 months of age has the potential to improve measles prevention in young infants, who are most vulnerable to the disease’s potentially devastating effects. However, some evidence on the age-specific effects of administering the first dose of a MCV (MCV1) to infants younger than 9 months suggests that its immunogenicity can be suboptimal, and subsequent MCV doses might not entirely compensate for this effect.

At the same time, another study notes that as passively acquired immunity through maternal antibodies ceases through the first 4 to 6 months of age, it renders the infant unprotected against measles, mumps, and rubella until the first MMR-vaccination at 9 months, and thus, optimisation of first MMR vaccination time point is of great importance.

If the timing of the MMR-vaccine is to be changed, it should be done only if there is the highest level of evidence that the MMR-vaccine elicits a sufficient immune response in the young infant resulting in improved immunity against MMR.

Virologist Dr. Gagandeep Kang says that in some settings six months is fine but will need at least one possibly two further doses because protection from the six months dose will be shorter than with the full doses of vaccine.

Dr. Shahid Jameel, another virologist who is also a Fellow at the Oxford Center for Islamic Studies, says that the measles vaccine can be given at 6 months in case there is an outbreak. But studies have shown subsequent lower measles antibody levels in such children possibly due to an immature immune system. Such children should be given the regular two doses of the MMR as per schedule.

But what is key at this juncture is to prevent the imminent measles epidemic. The situation is grave and the authorities should act before there is an explosion of cases.

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